Zinc plating bath and method

ABSTRACT

An aqueous bath for producing zinc electrodeposits upon metallic surfaces has a pH of 4.0 to 9.0 and contains zinc ion, chloride ion, and a surface-active constituent including at least one Nacylated sarcosine derivative. Preferably, the bath also contains one or more auxiliary surface-active agents, and it may in addition include brighteners, buffering agents, chelating agents, etc.

Beckwith et al.

[ ZINC PLATING BATH AND METHOD [75] Inventors: Merton M. Beckwith; Grace F. Hsu,

both of Rockville, Conn. [73] Assignee: Conversion Chemical Corporation,

Rockville, Conn.

[22 Filed: Oct. '26, 1971 21 Appl. No.2 192,624

[52 us. 01. 204/55 R, 204/55 Y [51] Int. Cl C23b 5/12 [58] Field of Search 204/55 R, 55 Y, DIG. 2

[56] References Cited UNITED STATES PATENTS 3,47l,27l 10/1969 Brown et al. 204/49 3,669,854 6/1972 l-larbulak 204/55 R 2,837,472 6/1958 Gundel et al. 204/49 2,986,498 5/1961 Strauss et al 204/46 3,075,899 H1963 Strauss et al 204/52 R [57] 7 An aqueous bath for producing zinc electrodeposits Jan. 22, 1974 3,296,104 1/1967 Eppensteiner 204 55 R 3,594,291 7/1971 Todt et al. 204/55 R FOREIGN PATENTS OR APPLICATIONS 1,263,445 3/1968 Germany 204/55 R 1,269,855 6/1968 Germany 204/55 R Primary Examiner--F. C. Edmundson Attorney, Agent, or Firm-Peter L. Costas ABSTRACT upon metallic surfaces has a pH of 4.0 to 9.0 and contains zinc ion, chloride ion, and a surface-active constituent including at least one N-acylated sarcosine derivative. Preferably, the bath also contains one or more auxiliary surface-active agents, and it may in addition include brighteners, buffering agents, chelating agents, etc.

21 Claims, No Drawings 1 ZINC PLATING BATH AND METHOD BACKGROUND OF THE INVENTION Various baths have in the past been widely employed for electroplating zinc upon metallic substrates; most commonly, such baths utilize cyanide or sulfate electrolytes, although it'has been suggested that other salts, such as the chlorides, may be used alone or in combination therewith. Generally, the cyanide baths have proven highly effective despite certain objectionable features, such as toxicity, difficulty of disposal, inadequate current efficiency, embrittlement of certain steels, difficulty of deposition upon cast and malleable irons, etc. The sulfate baths overcome many of the objectionable features of the cyanide baths, but exhibit ,low throwing power, poor efficiency at low current Another object is to provide such a bath which is effective. in depositing zinc upon cast and malleable irons, carbonitrided and other case-hardened ferrous metals, and which may produce bright deposits over a wide range of operating conditions.

A further object is to provide a novel method for electroplating zinc utilizing such an improved chloride bath by which there may be obtained highly advantageousadherent and ductile zinc deposits at relatively low cost.

SUMMARY OF. THE INVENTION It has now been found that the foregoing and related objects of the invention can be readily attained in an aqueous bath having a pH of about 4.0 to 9.0 and comprising at least one water-solublechlorine-containing compound in an amount sufficient to provide about 30.0 to 250.0 grams per liter of chloride ion, at least one water-soluble zinc compound in an amount sufficient to provide about 10.0 to 80.0 grams per liter of zinc ion, and about 1.0 to 30.0 grams per liter of a surface-active constituent including at least 0.25 gram per liter of at least one N-acylated sarcosine derivative having the formula:

In the above formula, R represents an aliphatic chain containingS to 21, andpreferably 11 to 16, carbon atoms, and M is a substituent selected from the class consisting of hydrogen, alkali metals, and the ammonium radical.

The bath may contain about 2.0 to 10.0 grams per liter of the sarcosine derivative. Preferably, it includes at least about 0.75 gram per liter of one or more auxiliary surface-active agents, which may be selected from the group consisting of sulfated polyoxyalkyl carbinamines, phosphoric acid esters of polyalkylene glycols and alkoxylated alkyl phenols, the alkali metal salts of such phosphoric acid esters, polyoxyalkyl carbinamines, imidazoline derivatives, polyoxyalkylated (alkyl)amines, fatty acid (alkyl)amine oxide derivatives, and mixtures thereof, the alkyl groups of such'agents containing 1 to 6 carbon atoms. Most desirably, the auxiliary agent is a mixture of a sulfated polyoxyalkyl carbinamine and an imidazoline derivative. In addition, the preferred bath may include 0.05 to 1.5 grams per liter of a brightener and about 10.0 to 100.0 grams per liter of a chelating agent, and it will have a pH of about 6.0 to 8.0.

Certain objects of the invention are attained in -a method for electroplating zinc wherein an aqueous bath having the composition previously set forth is first prepared. The bath is maintained at a temperature of about 20 to 70 Centigrade, and a workpiece having a metallic surface isimmersed therein together with a zinc anode. A potential is applied across the anode and workpiece to provide a current density of about 0.5 to 200.0 amperes per square foot (ASF) at the metallic surface, so as to deposit zinc thereon. In accordance with preferred embodiments of the method, the temperature at which the bath is maintained is about 25 to 40 Centigrade and the potential applied provides a current density of about 1.0 to 120.0 ASF. Most desirably, the preferred baths defined herein are employed in the practice of the method.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As has already been pointed out, the essential components of the present bath are zinc ion, chloride ion, and a surface active constituent including an N- acylated sarcosine derivative. Generally, other components, and especially auxiliary surface active agents and brighteners, will also be included in the bath, the composition of which will be discussed in detail hereinbelow.

The Sarcosine Derivatives In accordance with the concept of the invention, the surface active constitutent must include an N-acylated sarcosine derivative, which class of compounds is represented by the following structural formula:

in which, as has been previously indicated, the substituent designated R represents an aliphatic chain containing 5 to 21, and preferably 1 l to 16, carbon atoms and that designated M represents a hydrogen or alkali metal atom, or the ammonium radical. Typically, the acetyl moiety of the sarcosine derivative will be lauroyl, stearoyl, oleyl, and the like, and the compounds may be de rived from fatty acid mixtures, such as are, in turn, ob-

eral manufacturers and under a number of designations, including ARKOMON KA and KF, sold by Americal l-loechst Corporation; the HAMPOSYL series (e.g., C, C-30, L, L-30, sold by Hampshire Chemical Corporation; Onyx Chemical Companys -MAPROSYL 30; and the SARKOSYL series (e.g.,

NL97, NL-30, LC, L, O, S, T) sold by Geigy Chemical Corporation.

When employed by itself, the sarcosine derivative will normally be used in an amount of about 2.0 to 10.0, and preferably about 5.0 to 8.0, grams ,per liter. When it is employed in combination with an auxiliary surfactant, in accordance with preferred embodiments of the invention, the amount of the sarcosine derivative may be as low as 0.25 gram per liter, and it will not generally exceed 7.0 grams per liter. Preferably, when it is used in combination the amount of the sarcosine component will be from about 0.75 to 1.5 grams per liter.

The Auxiliary Surfactants Although a variety of auxiliary surfactants may be employed in combination with the sarcosine derivative, as will be specifically described hereinbelow, the sulfated polyoxyalkyl carbinamines and the imidazoline derivatives have been found to produce the best results. The sulfated polyoxyalkyl carbinamines precede the imidazolines in order of decreasing benefit, followed by the other members of the group of auxiliary surfactants identified. Optimum results are attained with combinations of at least two of the auxiliary surfactants together with the sarcosine derivative, and especially good results are realized when the combination includes a sulfated polyoxyalkyl carbinamine. Ideally, the surface active constituent of the bath will be a multi-membered mixture of the sarcosine derivative, a sulfated polyoxyalkyl carbinamine, and an imidazoline derivative. As has been previously pointed out, regardless of Whether the surface active constituent is provided by a 3.079.426, agent or by a combination thereof, the amount employed will generally be in the range of about 1.0 to 30.0 grams per liter. The concentration present in any particular bath will, of course, depend upon the specific composition of the bath and especially of the surface active constituent thereof.

When employed, the suflated polyoxyalkyl carbinamine will normally be present in the bath in a concentration of about 2.0 to 20.0 grams per liter, and preferably its concentration will be in the range of about 3.0 to 8.0 grams per liter. These compounds are amphoteric, and evidence stability for extended periods of time under normal plating conditions; generally, they are produced by sulfating the terminal hydroxyl group on the polyoxyalkyl chain and may be an alkali metal salt. It has been found that sulfated polyoxyalkyl tertcarbinamines having the following formula function especially well:

wherein R,, R and R are alkyl groups having a total of 7 to 23, and preferably 11 to 14, carbon atoms, m is a number from 8 to 25, and preferably from 12.5 to 17.5, and X is a monovalent cation selected from the class consisting of hydrogen and alkali metals. Surfaceactive agents of this type are described in detail in U.S. Pat. No. 3079,4 I 6, granted to Rohm & Huas Company on Feb. 26, 1963, as the assignee of Jean Dupre et a1.

When used in the absence of the sulfated polyoxyalkyl carbinamine, the other auxiliary surface-active agents may also be present in concentrations of about 2.0 to 20.0 grams per liter. However, they are most desirably employed in combination therewith, and under such circumstances their concentration will be about 0.2 to 3.0, and preferably about 0.3 to 1.0 grams per liter. The most effective of the auxiliary surfactants (aside from the sulfated carbinamines) have been found to be the imidazoline derivatives corresponding to the following general formula:

In the foregoing formula, R" represents an alkyl radical having 5 to 24 carbon atoms; G is the -OH group, an acid salt radical, an anionic surface-active sulfate salt radical such as preferably OSO OR, or an anionic surface-active sulfonate salt radical; and Z is --COOM, CH COOM, or C(OH)HCH SO M. The substituent designated M is a hydrogen atom, an alkali metal or an organic base, and that designated Y is either an OR' or N(R) A group. Each R substituent is independently selected from the group consisting of hydrogen, alkali metals, and (CH ),,COOM; A represents an anionic monovalent radical and n represents an integer from 1 to 4. Use of the dotted line representation for the bonds connecting the substituents G and CH Z to the nitrogen atom indicates that these substituents are optionally present or absent, but it should be understood that they are either both present or both absent. Desirable compounds are provided when, in accordance with the foregoing formula, G represents the group --OSO -OR, particularly in which R is a C to C alkyl group, and Z is a -COOM group in which M is preferably an alkali metal cation.

Exemplary of the compounds corresponding to the foregoing formula which are satisfactory for use in the baths described herein are 2-alkyl-l-(ethyl-betaoxypropanoic acid) imidazolines wherein the alkyl group is capryl, undecyl or a mixture of C -C chains, and the disodium salt of lauroyl-cycloimidinium-lethoxyethanoic acid-l-ethanoic acid.

An additional class of effective auxiliary surfactants are the anionic phosphate esters formed by reacting with phosphoric acid alkylene oxide condensates having the general formula:

wherein R is selected from the class consisting of alkoxy compounds having 10 to 15 carbon atoms in the alkyl portion thereof and alkyl phenoxy groups having 4 to 10 carbon atoms in the alkyl portion thereof. The alkoxy units are provided by a value of 5 to 25 for x. Generally, only one hydrogen will be replaced in the esterification reaction, although some minor portion of the reaction product may include esters wherein more than one hydrogen has been removed from the phosphoric acid. In addition to the acid esters produced by the reaction, the unsubstituted hydrogens may be replaced by alkali metals. An extensive description of the anionic phosphate esters is set forth in US. Pat. No. 3,310,496, granted Mar. 21, 1967, to Rohm & Haas Company, as assignee of Richard C. Mansfield, et al.

Another group of auxiliary surface-active agents which may be employed are the polyoxyalkyl carbinamines such as'are also described in the aforementioned Mansfield et al. US. Pat. No. 3,310,496. The carbinamines may also be sulfated or phosphated by reaction with a terminal hydroxy group on the polyoxyalkyl chain. Generally, the preferred carbinamines have the following formula:

wherein R is an allcoxy group having about to carbon atoms in the alkyl portion thereof or an alkyl phenoxy group having 4 to 10 carbon atoms in the alkyl portion thereof. R andR may be hydrogen or relatively short chain alkyl groups providing a total number of carbon atoms of at least one and less than eight. A particularly effective compound, which is believed to be the partially phosphated product of such a carbinamine, is sold by Rohm & Haas Company under the designation TRITON QS-30.

Still further auxiliary surface-active agents are the polyoxyalkylated (alkyl)amines such as the polyoxyethylated compound sold by General Aniline & Film Corporation under the designation KATAPOL PN-430, and the fatty acid (alkyl)amine oxide derivatives such as lauryl dimethyl'amine oxide, which is sold by Onyx Chemical Co. under the name AMMONYX LO. In the foregoing compounds, any alkyl groups present are believed to contain 1 to 6 carbon atoms in the chain.

The system may desirably also'include other surfaceactive agents, such as the polyalkoxylated alkyl phenols, natural phosphatides, alkyl amido betaines, the alkali metal salts of N-tallow beta-amino propionate, partial alkali metal salts of N-lauryl-betaiminopropionate and mixtures thereof.

The Zinc and Ammonium Compounds The bath may contain about 10.0 to 80.0 grams per liter of zinc ion, but the concentration thereof is preferably maintained within the range of about 20.0 to 55.0 grams per liter, and most desirably at about 30.0 to 45.0 grams per liter. Above about 80.0 grams per liter, the deposit tends to be semi-bright to matte grey; below about 10.0 grams per liter the deposit tends to be semibright over large areas and there is a tendency for burning to occur at high current densities. The zinc ion may be introduced as any appropriate soluble sinc compound and, although the use of zinc chloride is desirable from the standpoint of avoiding extraneous ions, zinc oxide is equally desirable and is readily available in substantially pure forms.

The chloride ion concentration is generally within the range of about 30.0 to 250.0 grams per liter; the concentration thereof will preferably be about 90.0 to 1500 grams per liter, and most desirably it will be about 1 10.0 to 130.0 grams per liter. Below about 30.0 grams per liter there is a tendency for the deposit to be semibright to matte grey, and the bath tends to exhibit reduced conductivity. Although the chloride ion is preferably introduced as ammonium chloride, because the ammonium radical is found to have a beneficial effect in the plating bath, it may be added as hydrochloric acid, zinc chloride, etc., if so desired. To obtain bright deposits over a broad range of current density, ammonium chloride should be present in an amount providing a molar ratio to the zinc salt of about 1:1 to 20:1. When the molar ratio of ammonium chloride to zinc salt is less than 1:1, the deposit tends to be semi-bright to matte grey. As will be appreciated, the values of 80.0

and 250.0 grams per liter for the concenrations of zinc and chloride ion, respectively, reflect solubility limitations and criteria for practical and economical operation, and not necessarily the outer limits of feasibility. The choice of the source for the chloride and zinc ions will normally be made to avoid interfering ions and on the basis of expense, and will be apparent to those skilled in the art in view of well-established chemical principles. As will be appreciated, a single compound, i.e., zinc chloride, can be used to furnish both the chloride and zinc ions in the bath.

Other Components Various brighteners may be used in combination with the surface-active agents to improve brightness to the extent of extreme specular reflectivity, including the aryl aldehydes, alkyl'aldehydes having a carbon chain of at least two carbon atoms, aromatic ketones, and

'1 ,2,3-benzotriazole. The term aryl aldehyde includes alkaryl aldehydes, and such alkyl and aryl aldehydes may be halogenated. Exemplary of such brighteners are o-anisaldehyde, p-anisic aldehyde bisulfite, furfural, glutaraldehyde, veratraldehyde, propionaldehyde, benzaldehyde, ortho-chlorobenzaldehyde, and parachlorobenzaldehyde. Aromatic ketones which may be used advantageously include benzylidene acetone, 4- benzoyl pyridine, and beta-cyclocitrylidene-acetone (beta-ionone), etc.; N-vinyl pyrrolidone has also been found to have a brightening effect in these baths.

The brightener is employed in a concentration of about 0.05 to 1.50 grams per liter. However, at concentrations greater than about 0.50 gram per liter there is a tendency for brighteners to be lost at low current densities, and there is also a tendency to diminish the levels of adherence and ductility of the plated deposit. Ac-

cordingly, the preferred range of brightener concentration is about 0.1 to 0.5 gram per liter. Particularly when the zinc ion concentration in the bath is greater than about 5.0 grams per liter and the chloride ion concentration is less than about 100.0 grams per liter, other substances have been found to exhibit some secondary brightening action, such .as polyvinyl alcohols, gelatin, animal glue, evaporated milk, etc. However, the best brighteners are those specified hereinbefore; of that group, 1,2,3-benzotriazole, and especially orthochlorobenzaldehyde, are most beneficial.

Buffering agents may be employed if desired to stabilize the pl-I of the film formed at the cathode and to maintain the pH value. within optimum limits for obtaining good quality deposits. Exemplary of such buffers are boric acid and acetic acid, and they are typically added in amounts of about 5.0 to 30.0 grams per liter.

Chelating agents are desirably employed to preventthe precipitation of basic zinc compounds either in the body of the plating bath or at the surface of the anode, and they also provide a buffering effect. Such chelating agents are added in amounts of 10.0 to 100.0 grams per liter, and preferably about 45.0 to 75.0 grams per liter, and include citric acid, malic acid, ethylene diamine tetraacetic acid, hydroxy ethylene diamine tetraacetic acid, diethylene triamine pentaacetic acid, nitrilotriacetic acid, and mixtures thereof.

Conditions of Operation The baths of the present invention may be operated at ambient temperatures (e.g., 20) and up to about 70 Centigrade. At low temperatures the plating operation tends to be inefficient. As the temperature is increased, there is a tendency for the minimum current density for satisfactory plating to increase, and for a simultaneous increase in the maximum current density at which satisfactory plating can be obtained. Undue consumption of brightener and evaporation also make operation at relatively high temperatures less desirable. Accordingly, the baths are preferably operated at a temperature of about 25 to 40, and most desirably at about 32 to 34, Centigrade.

The baths of the present invention are effective in a pH range of about 4.0 to about 9.0. However, at pH values near the lower end of the range, there is a tendency for darkening in the deposit at low current densities. Near the upper end of the pH range, milkiness and loss of brightness tend to result. Although these effects can be controlled somewhat by variations in the bath composition, from the standpoint of obtaining optimum results over a full range of current density, the baths are preferably operated at a pH of about 6.0 to 8.0. The pH may most appropriately be adjusted with citric acid, boric acid, ammonium hydroxide or hydrochloric acid to avoid the introduction of ions which might interfere with operation.

Various zinc anodes may be employed including pure zinc and the zinc alloys which are conventionally used in cyanide baths, e.g., zinc aluminum, zinc calcium and zinc magnesium. Since corrosion problems at the anode are materially reduced by the baths of the present invention, pure zinc anodes are highly advantageously employed. Moreover, it has been found that even small amounts of metallic impurities in the anodes, such as lead, iron and cadmium, can be readily solubilized with resultant interference in the optimum operation of the bath. Accordingly, highly refined anodes of high purity are most desirably utilized. Insoluble anodes are not desirable because of the possibility of generating nitrogen trichloride, which is highly explosive.

The baths of the present invention provide high conductivity and are operable at low voltages with high plating efficiencies; however, the current efficiency will tend to vary with the particular components selected and their ratios. For example, a Hull cell operated at three amperes requires the use of only about 2.2 volts with the preferred composition. The baths exhibit excellent throwing power over a wide range of current density, so that efficient plating of castings may be effected.

The current densities at which bright deposits are obtained will vary with the particular composition of the bath. Generally, the optimum formulations will provide bright deposits through a range of about 0.5 ASF to greater than 200.0 ASF, although a more practical operating range is about 1.0 to 120.0 ASF. Even with formulations which do not provide a bright deposit of specular reflectivity, adherent bright to dull m'atte deposits are obtained over a wide range. As indicated herein, acid baths may be desirable where high speed plating is required, whereas the neutral to alkaline baths are preferable where low current densities are to be encountered.

The process is adapted to both still plating and barrel plating apparatus with equal efficacy. Agitation is desirable to obtain deposits which are uniform and of high quality and to avoid development of anode sludge and film. Although rack plating may be effected in the substantial absence of agitation, movement of the bath, anode and/or workpiece has been found to be beneficial. Filtration of the bath is not essential but will normally be beneficial when contamination of the bath is encountered due to air-bome impurities and carry-over from other finishing operations. Various filtering media may be utilized including fabric, porous stoneware and other conventional filtering materials.

The depletion of the various components of the bath is best corrected by analysis for the several components on a periodic basis, which can be established for a given facility. To determine the necessity for the addition of surface-active agent(s), the surface tension of the bath may be measured from time to time, with quantities of surfactant being added when needed; ultimately, a suitable schedule of additions may be developed for the given facility. The ion content of a sample may be determined to enable calculation of amounts of zinc and chloride-containing compounds needed, and the amount of brightener required is best determined by testing a sample of the bath in a suitable cell.

Illustrative of the efficacy of the present invention are the following specific examples wherein all parts are parts by weight unless otherwise indicated.

Example One A zinc plating bath is prepared by admixing with water sufficient amounts of zinc oxide and ammonium chloride to provide therein 35.0 grams per liter of zinc .ion and 120.0 grams per liter of chloride ion, respectively. Also included in the bath are about 4.22 grams per liter of a sulfated polyoxyalkyl tert-carbinamine (TRITON QS-l5, Rohm & Haas Co.), about 1.13 grams per liter of lauroyl sarcosine (SARKOSYL L, Geigy Chemical Corporation), about 0.56 grams per liter of Z-caprylic-l-(ethyl-beta)-oxypropanoic imidazoline (MONATERIC CyA, Mona Industries, Inc.), about 1.4 grams per liter of an ethyleneglycol monoethylether (to assist solubility), about 0.2 gram per liter of ortho-chlorobenzaldehyde (as a brightener), and about 60.0 grams per liter of citric acid (as a chelating agent).

A portion of the resulting bath, which has a pH of about 7.3, is placed into a 267 milliliter Hull cell, and maintained at a temperature of about. 32 to 34 Centigrade. Utilizing a pure zinc anode and a clean steel panel, plating is effected for about three minutes by applying a potential across the anode and panel to produce a current of about three amperes. At the end of the plating period, the panel is removed from the cell and is inspected. The deposit thereon is found to be bright over a range of current density from about 1.0 to more than 120.0 ASF. The deposit is of excellent quality and is substantially free from pitting, cloudiness, burning or other surface imperfections; it is also found to be ductile and strongly adherent to the underlying panel.

Utilizing additional portions of the bath prepared above, the pll is adjusted to a lower value by the addition of hydrochloric acid, and to higher values by add? ing ammonium hydroxide. Thereafter, plating is effected in the manner described, and the plated panel is inspected as indicated.

At a pH of about 4.4, the deposit is found to be of marginal quality at current densities of about 1.5 ASP and below. Gray lines are present in the current density range of about 3.0 to 8.0 ASF, but from about 8.0 to more than 120.0 ASF the deposit is bright, albeit with slight graying in a narrow band at about 70.0 ASF. In addition, compared to the 7.3 pH bath, the present bath is found to have slightly diminished throwing power.

Adjusting the pH to about 8.2 results in the presence of a. somewhat milky film at current densities of about 15.0 ASF andbelow. Above about 90.0 ASF the deposit is somewhat gray, but in the intermediate range of current density the deposit is bright and of high quality. The throwing power of this bath is notably better than that of the 4.4 pH formulation.

Finally, adjusting the pH to a value of about 9.0 results in slight cloudiness over the entire plated panel. Nevertheless, a satisfactory milky-bright deposit is produced at current densities between about 25.0 and 100.0 ASF. Below about 25.0 ASF the deposit exhibits a white dullness, whereas above about 100.0 ASF considerably grayness is in evidence.

Example Two Part A A zinc plating bath is prepared with substantially the same components and concentrations thereof as are used in the 7.3 pH bath of Example One, except that lauroyl sarcosine provides the sole surface-active agent therein (i.e., the carbinamine and imidazoline compounds are omitted), and that the amount thereof is increased to about 7.5 grams per liter. After plating a steel panel in the manner previously described, it is removed from the cell and inspected. Within the range of about 1.5 to 60.0 ASF, a bright and good quality deposit is obtained; from about 60.0 to almost 120.0 ASF the quality of the deposit is fair, although somewhat gray and dull; below about 1.5 ASF'the deposit is of quite poor quality. The fair and good quality deposits are found to be ductile and highly adherent to the underlying steel panel. I

Part B Part C To the bath of Part A is added about 4.0 grams per liter of the sulfated polyoxyalky. tertiary carbinamine surface-active agent employed in Example One. The bath isfound to produce a bright, high quality deposit within a range that is broader than that produced in Part A hereof, but which does not extend toquite as One. As in the previous instances, the deposit produced is ductile and adherent to the underlying substrate.

Example Three vides a novel chloride plating bath for producing adherent and ductile zinc deposits. The bath is operable over a wide range of current density with high current efficiency, and it is capableof producing bright deposits under a variety of operating conditions. It also affords excellent throwing power and high levels of effectiveness at low voltage, and it is effective in depositing zinc upon cast and malleable irons and upon carbonitrided and otherwise case-hardened ferrous metals. The invention also provides a novel method for electroplating zinc utilizing such an improved chloride bath to obtain highly advantageous adherent and ductile zinc deposits at relatively low cost.

Having thus described the invention, we claim:

1. An aqueous bath for producing a zinc electrodeposit comprising: at least one water-soluble chlorinecontaining compound selected from the group consisting of zinc chloride, ammonium chloride, and mixtures thereof in an amount sufficient to provide about 30.0 to 250.0 grams per liter of chloride ion; at least one water-soluble zinc compound in an amount sufficient to provide about 10.0 to 80.0 grams per liter of zinc ion; and about 1.0 to 30.0 grams per liter of surfaceactive constitutent including at least 0.25 gram per liter of at least one N-acylated sarcosine derivative having the formula:

wherein R represents an aliphatic chain containing 5 to 21 carbon atoms, and wherein M is a substituent selected from the class consisting of hydrogen, alkali metals, and the ammonium radical, said bath having a pH of about 4.0 to 9.0.

' 2. The bath of claim 11 wherein said bath contains about 2.0 to 10.0 grams per liter of said sarcosine derivative.

3. The bath of claim 1 wherein said surface-active constituent includes at least about 0.75 gram per liter of at least one auxiliary surface-active agent selected from the group consisting of sulfated polyoxyalkyl carbinamines, phosphoric acid esters of polyalkylene glycols and alkoxylated alkyl phenols and the alkali metal salts of such phosphoric acid esters, polyoxyalkyl carbinamines, imidazoline derivatives, polyoxyalkylated alkyl)amines, and fatty'acid (alkyl )amineoxide derivatives, the alkyl groups of said (alkyl)amine and (alkyl) amine oxide derivatives containing 1 to 6 carbon atoms.

41. The bath of claim 3 wherein said auxiliary agent is a mixture of a sulfated carbinamine and an imidazoline derivative.

5. The bath of claim 3 wherein said sulfated carbinamine has the formula wherein R R and R are alkyl groups having a total of 7 to 23 carbon atoms therein, m is a number from 8 to 25 and X is a monovalent cation selected from the class consisting of hydrogen and alkali metals.

6. The bath of claim 3 wherein said imidazoline derivative corresponds to the formula:

wherein:

1. R is an alkyl radical having to 24 carbon atoms;

2. G is a radical selected from the group consisting of OH, acid salt radicals, anionic surface-active sulfate salt radicals, and anionic surface-active sulfonate salt radicals;-

3. Z is a radical selected from the group consisting of COOM, CH COOM, and HO-Cl-lCl-l- 2 3 4. M is a substituent selected from the group consisting of hydrogen, alkali metals and organic bases;

5. Y is selected from the group consisting of OR and N(R') A;

6. each R substituent is independently selected from the group consisting of hydrogen, alkali metals, and (CH2)n COOM;

7. A is an anionic monovalent radical;

8. n is an integer from 1 to 4; and

9. both the groups G and CH Z are present or absent.

7. The bath of claim 1 wherein said chloride ion and zinc ion are present in amounts of about 90.0 to 150.0 and 20.0 to 55.0 grams per liter, respectively, and wherein R in said sarcosine derivative represents an aliphatic chain containing 11 to 16 carbon atoms.

8. The bath of claim 1 wherein said chloride ion and zinc ion are present in amounts of about 1 10.0 to 130.0 and 30.0 to 45.0 grams per liter, respectively.

9. The bath of claim 1 wherein said pH is about 6.0 to 8.0.

10. An aqueous bath for producing a zinc electrodeposit comprising: at least one water-soluble chloridecontaining compound in an amount sufficient to provide about 30.0 to 250.0 grams per liter of chloride ion; at least one water-soluble -zinc compound in an amount sufficient to provide about 100 to 80.0 grams per liter of zinc ion, and, as a surface-active constituent, about 1.0 to 30.0 grams per liter of a mixture of surfaceactive agents comprising:

a. at least 0.25 gram per liter of at least one N-acetyl sarcosine derivative having the formula:

wherein R represents an aliphatic chain containing 5 to 21 carbon atoms, and wherein M is a substituent selected from the class consisting of hydrogen, alkali metals, and the ammonium radical; and

b. at least 0.75 gram per liter of an auxiliary agent selected from the group consisting of sulfated polyoxyalkyl carbinamines, phosphoric acid esters of polyalkylene glycols and alkoxylated alkyl phenols and the alkali metal salts of such esters, polyoxyalkyl carbinamines, imidazoline derivatives, polyoxyalkylated (alkyl)amines, fatty acid (alkyl)amine oxide derivatives, and mixtures thereof;

said bath having a pH of 4.0 to 9.0.

11. The bath of claim 10 wherein said chloride ion and zinc ion are present in amounts of about 90.0 to 150.0 and 20.0 to 55.0 grams per liter, respectively, and wherein R in said sarcosine derivative represents an aliphatic chain containing 11 to 16 carbon atoms.

12. The bath of claim 10 wherein said auxiliary agent of said surface-active constituent is a mixture of a sulfated polyoxyalkyl carbinamine and an imidazoline derivative.

13. The bath of claim 12 containing the following additional components: 0.05 to 1.5 GRAMS PER LITER OF A brightener selected from the group consisting of aryl aldehydes, alkyl aldehydes having a carbon chain of at least two carbon atoms aromatic ketones, and 1,2,3-benzotriazole, and 10.0 to 100.0 grams per liter of a chelating agent selected from the group consisting of citric acid, malic acid, ethylene-diamine tetraacetic acid, hydroxyethylenediamine tetraacetic acid, diethylenetriamine pentaacetic acid, nitrilotriacetic acid, and mixtures thereof.

14. The bath of claim 13 having the following formulation:

ammonium chloride (as chloride) 1 10 to 130 g/l zinc compound (as metal) 30 to g/l sulfated polyoxyalkyl ten-carbinamine 3 to 8 g/l imidazoline derivative 0.3 to 1.0 g/l sarcosine derivative 0.75 to 1.5 g/l brightener 0.1 to 0.5 g/l chelating agent to 70 g/l said bath having a pH of about 6.0 to 8.0.

15. The bath of claim 14 wherein said sarcosine derivative is lauroyl sarcosine and said imidazoline derivative is 2-caprylic-l-(ethyl-beta)-oxypropanoic imidazoline.

16. In a method of electrodepositing zinc, the steps comprising:

a. preparing an aqueous bath comprising at least one water-soluble chlorine-containing compound selected from the group consisting of zinc chloride, ammonium chloride, and mixtures thereof in an amount sufficient to provide about 30.0 to 250.0 grams per liter of chloride ion, at least one watersoluble zinc compound in an amount sufficient to provide about 10.0 to 80.0 grams per liter of zinc ion, and about 1.0 to 30.0 grams per liter of surface-active constituent including at least 0.25 grams per liter of at least on N-acetyl sarcosine derivative having the formula:

wherein R represents an aliphatic chain containing to 21 carbon atoms, and wherein M is a substituent selected from the class consisting of hydrogen, alkali metals, and the ammonium radical, said bath having a pH of 4.0 to 9.0;

b. maintaining said bath at a temperature of about 20 to 70 Centigrade;

c. immersing in said bath a workpiece having a metallic surface and a zinc anode; and

d. applying a potential across the anode and workpiece to deposit zinc on said metallic surface, said potential providinga current density of about 0.5

to 200.0 amperes per square foot at said metallic surface.

17. The method of claim 16 wherein said temperature is about 250 to 40 Centigrade, and wherein said potential provides a current density of about 1.0 to 120.0 amperes per square foot.

18. The method of claim 16 wherein said bath contains about 2.0 to 10.0 grams per liter of said sarcosine derivative.

19. The method of claim 16 wherein said surfaceactive constituent includes at least about 0.75 gram per liter at least one auxiliary surface-active agent selected from the group consisting of sulfated polyoxyalkyl careeiaaqxiqq. der va ve c a ni g, ,29v 6. ca bon,

atoms.

20. The method of claim 16 wherein said bath has the following formulation:

ammonium chloride (as chloride) to g/l zinc compound (as metal) 30 to 45 g/l sulfated polyoxyalkyl tert-carbinamine 3 to 8 g/l imidazoline derivative 0.3 to 1.0 g/l sarcosine derivative 0.75 to 1.5 g/l brightener 0.1 to 0.5 g/l chelating agent said bath having a pH of about 6.0 to 8.0.

21. The method of claim 20 wherein in said bath said brightener is ortho-chlorobenzaldehyde, said sarcosine derivative is lauroyl sarcosine, and said imidazoline derivative is 2-caprylic-l-(ethyl-beta)-oxypropanoic imidazoline. 

2. G is a radical selected from the group consisting of -OH, acid salt radicals, anionic surface-active sulfate salt radicals, and anionic surface-active sulfonate salt radicals;
 2. The bath of claim 1 wherein said bath contains about 2.0 to 10.0 grams per liter of said sarcosine derivative.
 3. The bath of claim 1 wherein said surface-active constituent includes at least about 0.75 gram per liter of at least one auxiliary surface-active agent selected from the group consisting of sulfated polyoxyalkyl carbinamines, phosphoric acid esters of polyalkylene glycols and alkoxylated alkyl phenols and the alkali metal salts of such phosphoric acid esters, polyoxyalkyl carbinamines, imidazoline derivatives, polyoxyalkylated (alkyl)amines, and fatty acid (alkyl)amine oxide derivatives, the alkyl groups of said (alkyl)amine and (alkyl)amine oxide derivatives containing 1 to 6 carbon atoms.
 3. Z is a radical selected from the group consisting of -COOM, -CH2COOM, and HO-CH-CH2SO3M;
 4. M is a substituent selected from the group consisting of hydrogen, alkali metals and organic bases;
 4. The bath of claim 3 wherein said auxiliary agent is a mixture of a sulfated carbinamine and an imidazoline derivative.
 5. Y is selected from the group consisting of -OR'' and -N(R'')3A;
 5. The bath of claim 3 wherein said sulfated carbinamine has the formula
 6. The bath of claim 3 wherein said imidazoline derivative corresponds to the formula:
 6. each R'' substituent is independently selected from the group consisting of hydrogen, alkali metals, and -(CH2)n-COOM;
 7. A is an anionic monovalent radical;
 7. The bath of claim 1 wherein said chloride ion and zinc ion are present in amounts of about 90.0 to 150.0 and 20.0 to 55.0 grams per liter, respectively, and wherein R in said sarcosine derivative represents an aliphatic chain containing 11 to 16 carbon atoms.
 8. The bath of claim 1 wherein said chloride ion and zinc ion are present in amounts of about 110.0 to 130.0 and 30.0 to 45.0 grams per liter, respectively.
 8. n is an integer from 1 to 4; and
 9. both the groups G and CH2Z are present or absent.
 9. The bath of claim 1 wherein said pH is about 6.0 to 8.0.
 10. An aqueous bath for producing a zinc electrodeposit comprising: at least one water-soluble chloride-containing compound in an amount sufficient to provide about 30.0 to 250.0 grams per liter of chloride ion; at least one water-soluble zinc compound in an amount sufficient to provide about 10.0 to 80.0 grams per liter of zinc ion, and, as a surface-active constituent, about 1.0 to 30.0 grams per liter of a mixture of surface-active agents comprising: a. at least 0.25 gram per liter of at least one N-acetyl sarcosine derivative having the formula:
 11. The bath of claim 10 wherein said chloride ion and zinc ion are present in amounts of about 90.0 to 150.0 and 20.0 to 55.0 grams per liter, respectively, and wherein R in said sarcosine derivative represents an aliphatic chain containing 11 to 16 carbon atoms.
 12. The bath of claim 10 wherein said auxiliary agent of said surface-active constituent is a mixture of a sulfated polyoxyalkyl carbinamine and an imidazoline derivative.
 13. The bath of claim 12 containing the following additional components: 0.05 to 1.5 GRAMS PER LITER OF A brightener selected from the group consisting of aryl aldehydes, alkyl aldehydes having a carbon chain of at least two carbon atoms aromatic ketones, and 1,2,3-benzotriazole, and 10.0 to 100.0 grams per liter of a chelating agent selected from the group consisting of citric acid, malic acid, ethylene-diamine tetraacetic acid, hydroxyethylenediamine tetraacetic acid, diethylenetriamine pentaacetic acid, nitrilotriacetic acid, and mixtures thereof.
 14. The bath of claim 13 having the following formulation:
 15. The bath of claim 14 wherein said sarcosine derivative is lauroyl sarcosine and said imidazoline derivative is 2-caprylic-1-(ethyl-beta)-oxypropanoic imidazoline.
 16. In a method of electrodepositing zinc, the steps comprising: a. preparing an aqueous bath comprising at least one water-soluble chlorine-containing compound selected from the group consisting of zinc chloride, ammonium chloride, and mixtures thereof in an amount sufficient to provide about 30.0 to 250.0 grams per liter of chloride ion, at least one water-soluble zinc compound in an amount sufficient to provide about 10.0 to 80.0 grams per liter of zinc ion, and about 1.0 to 30.0 grams per liter of surface-active constituent including at least 0.25 grams per liter of at least on N-acetyl sarcosine derivative having the formula:
 17. The method of claim 16 wherein said temperature is about 25.0* to 40* Centigrade, and wherein said potential provides a current density of about 1.0 to 120.0 amperes per square foot.
 18. The method of claim 16 wherein said bath contains about 2.0 to 10.0 grams per liter of said sarcosine derivative.
 19. The method of claim 16 wherein said surface-active constituent includes at least about 0.75 gram per liter at least one auxiliary surface-active agent selected from the group consisting of sulfated polyoxyalkyl carbinamines, phosphoric acid esters of polyalkylene glycols and alkoxylated alkyl phenols and the alkali metal salts of such phosphoric acid esters, polyoxyalkyl carbinamines, imidazoline derivatives, polyoxyalkylated (alkyl)amines, and fatty acid (alkyl)amine oxide derivatives, the alkyl groups of said (alkyl)amine and (alkyl)amine oxide derivatives containing 1 to 6 carbon atoms.
 20. The method of claim 16 wherein said bath has the following formulation:
 21. The method of claim 20 wherein in said bath said brightener is ortho-chlorobenzaldehyde, said sarcosine derivative is lauroyl sarcosine, and said imidazoline derivative is 2-caprylic-1-(ethyl-beta)-oxypropanoic imidazoline. 